1. Field of the Invention
The present invention is related to rotary motion sensors and, more particularly, is directed towards a rotary motion sensor which employs an endless multiple turn fiber interferometer.
2. Description of the Prior Art
As pointed out in my copending U.S. application Ser. No. 813,362, filed July 6, 1977, fiber interferometers have recently come into their own as means for measuring the rate of rotation of bodies based upon the Sagnac interferometer effect.
In my copending application, I describe a practical, fieldworthy rotary motion sensor which employs a fiber interferometer having first and second ends into which coherent radiation from a fiber laser is inserted in clockwise and counter-clockwise directions. After the coherent radiation has made one traversal of the multiple turn optical waveguide, the respective clockwise and counterclockwise signals, phase shifted in proportion to the rotational rate of the system, are extracted from the fiber interferometer and are fed to a pair of heterodyne detectors. Also fed to each detector is a reference signal which comprises the laser frequency offset by an acoustic frequency, the latter being provided by an acousto-optic grating which serves to offset and couple the coherent radiation to the detectors. The output from the respective detectors comprise a pair of signals at the acousto-optic drive frequency which have the same phase relationship as the coherent optical signals. The relative phase between the two acoustic signals may be detected by conventional electronics to provide a measure of the rotation rate of the system.
While the system set forth in my copending application as described above is advantageous over the prior art, the resolution and accuracy achievable by same is somewhat limited due to the relatively small phase shifts effectuated in the coherent signals as they traverse the multiple turn optical waveguide only a single time apiece. The very small phase shifts can lead to not inconsiderable errors in detection and measurement. It would clearly be desirable if a system could be provided in which larger phase shifts of the counter-rotating radiation could be achieved to therefore increase the precision and accuracy of the measurement technique. It is toward this end that the present invention has been advanced.